Báo cáo khoa học: "Effects of lime-induced differences in site on fine roots of oak"

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Original article Effects of lime-induced differences in site fertility on fine roots of oak Nys’ Mark R. Bakker Claude Équipe cycles biogéochimiques, Inra Nancy, 54280 Champenoux, France (Received 9 March 1999 ; accepted 9 June 1999) Abstract - This study aims at evaluating the effects of lime-induced differences in site fertility on fine roots. Lime was applied to ten oak (Quercus petraea and Q. robur) stands on acidic soils with low base saturation, 1-27 years before fine root sampling. The soil exchangeable nutrient pool, fine root and foliar composition all showed deficient levels for at least a number of elements. Liming enhanced fine root biomass both in topsoil and in deeper horizons, and overall fertility and nutrition were improved for Ca and Mg but not for K and P. Thus, liming in moderate doses on acidic sites showing nutrient deficiencies may stimulate the absorbing capaci- ty of the tree root system by enlarging fine root standing crop and thereby improving uptake of mineral nutrients and stand growth. However, one should bear in mind that resolving a deficiency for some elements can create less favourable conditions for others. © 1999 Éditions scientifiques et médicales Elsevier SAS. fine roots / liming / mineral nutrition / Quercus / soil Résumé - Conséquences, après amendement, d’un changement de fertilité sur les racines fines de chêne. Cette étude évalue l’effet des changements induits au niveau de la fertilité du sol par des amendements calciques et ses conséquences sur les racines fines. Les amendements calciques ont été appliqués dans dix peuplements de chêne (Quercus petraea et robur) sur des sols acides et désaturés, entre1 et 27 ans avant l’échantillonnage des racines fines. Ces dix peuplements montraient des déficiences nutritives déterminées par le niveau des stocks d’éléments échangeables, la composition minérale des racines et des feuilles. Les amendements ont augmenté la biomasse racinaire en surface et en profondeur et la nutrition de Ca et Mg, mais pas celle de P et K. Un amendement calcique modéré, sur des sols acides avec des déficiences nutritives, peut ainsi stimuler le système d’absorption de l’arbre en aug- mentant la biomasse racinaire, et secondairement la nutrition minérale et la croissance des arbres. Il est important de signaler que l’effet sur d’autres éléments nutritifs, non apportés, peut être moins favorable et même déséquilibrer le système dans un autre sens. © 1999 Éditions scientifiques et médicales Elsevier SAS. calcique / nutrition minérale / Quercus / racine fine / sol amendement cient level of nutrient resources in the soil (in plant- 1. Introduction available form) is needed to ensure a sustained produc- tivity and vitality of the forest stands. Uptake of Mg 2+ evaluating forest productivity, For the purpose of or Ca can be strongly depressed when in competition 2+ and soil resources, the interface between soil vitality with other cations such as K NH Al or H [14]. + 4 3+ + ,+ , nutrient pools and tree roots as uptake organs to sustain Thus, not all of the potentially available soil nutrients above-ground growth, is of utmost importance. A suffi- * Correspondence and reprints tel: + 33 (0)3 83 39 40 73 ; fax: (0)3 83 39 40 69 33 + e-mail: nys@nancy.inra.fr
Netherlands (sites 9 and 10). The lime treatments were in accessibleto tree roots owing to such an antagonistic are form of CaCO or CaO. In addition to the lime amend- A way of evaluating the root function, that uptake [15]. 3 is root health and thus uptake potential, is the use of ment some complementary compounds were used: N Ca/Al ratios in the tissue of fine roots [1, 6]; Ca/Al ratios (sites 4-6), N, P and K (site 8) and Mg (3.5 % in the below the threshold levels indicate potential toxicity and lime product on sites 9 and 10). The levels of these addi- physiological disturbance. As allocation of nutrients, tions were low, especially for the N which was only applied in the oldest sites (26-27 years ago), and it was after uptake, is often preferential to the canopy relative to the roots, fine roots can be good additional indicators assumed that it would not have an influence on the pre- of change in nutritional conditions in forest stands [12]. sent tree response [3]. Soil and fine roots were sampled by soil coring down to a maximum of 75 cm (table I) They can be very useful as stress indicators at an early stage before major deficiencies can be detected at the and were treated separately for each soil layer (generally foliar level [8, 20]. Ten oak stands mostly situated on layers of 15 cm with the first layer separated into 0-5 poor acidic forest soils were included in this study. They and 5-15 cm), although summed values or averages over the total profile were sometimes used as an additional featured deficiencies for one or more nutrients (amongst which Ca was generally deficient). Lime as a "compen- variable. Sample number was generally between two and sation amendment" was expected to increase fertility and four per soil layer and treatment for chemical analyses productivity of these stands. The objective of this paper (soil and fine roots) and between 16 and 18 for fine roots was to determine the lime-induced changes in soil fertili- (weight, length), but this varied for the different experi- mental sites. Foliage was sampled in August close to the ty and total mineral nutrition of trees and their relation- ship to fine root development. In a previous paper [1]the top of the crown of five dominant trees per experimental effects of liming on soil chemistry, element concentra- plot and above-ground tree growth was evaluated by tions in roots and foliage, fine root development and means of height, diameter at breast height (DBH) and stand growth were described. Here, the focus is more on analysis of ring width on wood cores. general site fertility and nutrition. All individual samples (per point and layer) were processed separately. Soil samples were air-dried and then sieved at 2 mm. ICP (emission spectrometry) was 2. Materials and methods used to determine 0.5 M NH Al, Ca, Cl-exchangeable 4 Mg, K, Mn and Na [17], automatic titration to determine Between June 1994 and March 1996 a total of ten dif- exchangeable acidity [17], and pH-electrodes to deter- ferent sites with Oak (Quercus petraea and Q. robur) mine pH-KCl and pH-H following standard proce- O 2 were sampled for measurement of soil, fine root, foliage dures and a 1:2.5 dilution basis. Concentrations were and above-ground growth parameters. Eight of the trials expressed on an oven-dried (105 °C) weight basis. The are situated in France and two in the south-east of the fine roots (< 2 mm in diameter) were separated from the
soil by wet sieving above a 4- and 2-mm sieve followed in the fine roots by the dry weight of fine roots per soil short flotation to rinse the roots and root length was layer, before summing these values on a hectare and pro- by file basis. Since sampling was carried out only for a lim- estimated by the line intersection method [16]. The fine ited number at the deepest layers, these summed values root dry weight was obtained by drying at 105 °C to con- stant weight. Correction factors for losses due to stock- were not tested for treatment effects. Instead, treatment effects were established by analysis of variance within ing, and passing through the sieve were established and evaluated at +20 % for weight and at +25 % for length. individual horizons. The Student-Newman-Keuls test For the chemical analyses of foliage and fine roots, sub- was used to establish significant differences between samples were pre-treated with peroxide (H then group means with Unistat 4.0 software [18]. ), O 2 mineralized with HClO and analysed by ICP. For addi- 4 tional information on the methods, see Bakker [1]. 3. Results The amounts of exchangeable nutrients in the soil calculated by multiplying the concentration deter- were mined on soil samples by the average soil density of the The quantities of exchangeable elements are presented in table II and figure 1. The quantity of exchangeable Ca different layers. These soil densities were either known and Mg was increased by liming, but this was noticeable or estimated using general site characteristics such as texture and soil density values for similar sites in the only in the most recently limed stands. All together, Renecofor sites [5]. The amounts of nutrients in fine based on individual horizons, this increase in Ca was sig- nificant only for the most recently limed stands. An roots were calculated by multiplying the concentrations
apparent decrease in exchangeable Ca at sites 3 and 5 is 0.03), of K (0.93± 0.03 and 0.87 ± 0.05) and P (0.51 ± due to a lime-rich layer in the subsoil, explaining the 0.03 and 0.51 ± 0.03) were not clearly affected [1]. ± high total values of Ca in the control plots; in the top lay- The parts of the soil profile below the Ca/Al thresholds ers liming increased the total amount of Ca. Effects of [1, 6] of the tissue of the fine roots in the control and liming on K were less clear: some increases and some lime treatments and the net effects of liming are present- decreases. The total amounts of K may have declined ed in table IV. It shows that at most of the sites fine root critical Ca/Al ratios occur in at least a part of the soil slightly. profile [6], and that liming increased this Ca/Al ratio in The total amount of Mg and Ca in the fine roots (table many soil layers. III) was increased in most cases (for seven out of ten sites), although this failed to be significant in most According to absolute nutrient levels [3, 19], liming stands owing the limited sample number per soil only succeeded in improving foliar nutrition out of the to layer; effects on P and K were not conclusive. The con- critical range for Ca, and occasionally for Mg (table V). centrations of these elements in the fine roots showed a This lime-induced increase in foliar Ca and Mg was con- marginal increase as shown by the overall mean values sistent throughout all liming trials, and only slightly ( ± standard errors) for Ca (2.3 ± 0.22 and 2.6 ± 0.27 g lower for the sites with the greatest time lapse since lim- -1 kgdry weight for control and liming, respectively), ing. The Ca/N and Mg/N values show the same lime- whereas concentrations of Mg (0.95 ± 0.04 and 0.98 induced stimulation and consistency over time.
However, for P and K, the values relative for root Ca and Mg as compared to foliar N (increase by to N were less absolute foliar levels. Absolute levels than liming), showing no nutritional disturbances [4, 20]. The positive were showed some decrease in P level (six sites decrease, one decrease in Ca/N and Mg/N ratios for site 8 may be due increase, three no effect) and there was no clear effect on to the fact that N was also added on that particular site. K (five sites increase, five sites decrease). The values on the values of the ratio of root Thus, the effect of lime relative to N indicated a decrease in eight out of ten for Ca and root Mg to foliar N closely resemble those for the P/N and some changes in K/N ratios for the oldest lime ratios of foliar to foliar N levels (table V). For the P/N trials in particular. The increase in P/N occurred princi- and K/N ratios this was different (figure 2). As can be pally at site 8, where some P was supplied with the lime seen in this figure, for the P/N ratios, the effect of liming treatment. Most of the values relative to N are normal (expressed as nutrient level relative to N) is not very evi- compared to the values given by Boxman et al. [4] dent in the fine roots (no clear tendency), but in the (Mg/N ≥ 5, K/N ≥ 25 and P/N ≥ 5) or close to normal foliage the P/N ratios (indicated by the symbols) tend to with low values at sites 3 (P/N) and 1 and 2 (Mg/N). decrease after liming. For the K/N ratios the opposite is true: the foliar/foliar ratio is not clearly affected by lim- concentrations of nutrients relative The fine root to ing (indicated by the symbols), while the root/foliar foliar N are presented in table VI, as the dataset for root complete. The values are in general positive ratios tend to decrease. N not was
4. Discussion had a poor Ca nutrition after liming) and for Mg to a cer- tain extent (and largest on the two sites where some Mg was present in the lime product). This improvement in The adaptation of root systems to acidic soils can be fertility level for Ca and Mg was most pronounced in the achieved either by an efficient nutrient uptake, efficient first years after liming (table II, figure 1). The availabili- utilisation of nutrients or both [10]. At poor sites alloca- ty of K (poor on four sites) and of P (poor on seven sites) tion of assimilates to fine roots is generally higher [11], was not improved. The lack of data on P levels in the for example when N, P or S are deficient [9]. soil after liming did not permit an evaluation of the lim- Conversely, when subsoil acidification enhances Mg or ing effects for P in the soil directly, so that the foliar Ca deficiency due to an imbalance in uptake, an analyses (table V) were used to infer the absence of a P improvement of fertility and alkalinity (by lime) may effect after liming. increase fine root growth [9]. In the ten oak stands included in this work, liming generally stimulated fine Root health appeared to be improved by liming, as root development and stand growth and these effects shown by the increased Ca/Al ratio [6], a higher were detectable until at least 20-25 years after the lime live/dead ratio of fine roots in the initial years after lim- treatments [1]. Whether this stimulation is the result of a ing and indications of a higher root life-span [1]. The resolved deficiency or conversely an investment optimis- Ca/Al molar ratio in the fine roots expresses the inability ing uptake of nutrients that are most deficient [7], or ability to take up nutrients owing to presence or depends on the general soil fertility and the way these absence of Al stress. In this study, toxic Ca/Al ratios of nutrients are transported to the roots [21]. 0.10-0.20 [6, 13] were alleviated by liming down to a The soil chemical status was improved by liming, as depth of 30 or even 45 cm and concomitantly, root described in more detail in a previous paper [1]. Liming growth was not only stimulated in topsoil, but also in the increased exchangeable Ca, Ca/Al ratio, base satura- 3+ deeper layers. tion, CEC, pH-H and pH-KCl, and decreased soil Na, O 2 3+ Al and H effects on Mg, K, S and Mn were negligi- ; + Thus, the higher Ca availability improved fine root ble. As compared with the threshold levels [3] for soil health, amount of fine roots, tree growth and Ca nutrition fertility, seven stands were originally poor or very poor (in fine root tissue and in foliage). Mg was also stimulat- in Ca, four stands were very poor in Mg, four poor or ed to a smaller extent and not only at the sites where very poor in K and six (probably seven) poor or very some Mg was in the lime product. Effects on N nutrition poor in P. Liming improved this clearly for Ca (four sites were a decrease of foliar N by lime at first, followed by
fine root health (as indicated by higher live/dead and increase over time. The fine root contents of P an showed a decrease in the most recently limed plots and Ca/Al ratios of fine roots). It could also be a response to low P and K levels, as shown by low total levels of these in the foliage there was a general decrease in P content. elements in the soil and the nutrient ratios in To evaluate disequilibria in nutrition, values expressed relative to nitrogen [4] and foliar to root levels are means foliage/foliage and foliage/root relative to N. of detecting potential stress at an early stage [20]. Changes in root concentrations may occur before those in foliage, so that fine root chemical analyses may be References powerful indicators of mineral deficiencies at an early indicators of sus- [1] Bakker M.R., Fine-root parameters stage. Following such comparisons, there were no nutri- as 122 (1999) of forest ecosystems, For. Ecol. tainability Manage. tional disequilibria for Ca or Mg after liming (tables V 7-16. and VI, figure 2). In contrast, they indicated retention of [2] Bakker M.R., Garbaye J., Nys C., Effect of liming on P relative to N in the fine roots, rather than a preferential the ectomycorrhizal status of oak, For. Ecol. Manage. (1999) in transport to the foliage as is the case for K. As the leaves press. for analysis are collected in the top of the crown, this [3] Bonneau M., Fertilisation des forêts dans les pays tem- may suggest that part of the crown and the root system pérés. Théorie, bases du diagnostic, conseils pratiques, réalisa- can be low in K already owing to dilution to the upper tions expérimentales, Engref, Nancy, 1995, 366 p. crown parts. Thus, P and K nutrition may become defi- Boxman A.W., Cobben P.L.W., Roelofs J.G.M., Does [4] cient in the long term. to recovery of tree health in a (K+Mg+Ca+P) fertilization lead nitrogen stressed Quercus rubra L. stand?, Environ. Pollut. 85 Since Ca and Mg are less limiting after liming, the (1994) 297-303. observed greater amount of fine roots after liming could [5] Brêthes A., Ulrich E., Renecofor - Caractéristiques be an adaptation to low P and K levels. These are both pédologiques des 102 peuplements du réseau, Office national elements for which diffusion processes are more impor- des forêts, dép. recherches techniques, 1997, 573 pp. tant for transport to the root than mass flow, so that an [6] Cronan C.S., Grigal D.F., Use of calcium/aluminium increase in the soil volume explored by fine roots is ratios indicators of stress in forest ecosystems, J. Environ. as directly related to a higher access to P and K sources Qual. 24 (1995) 209-226. [21]. In accordance with this, Ca is important for cell [7] Eissenstat D.M., Yanai R.D., The ecology of root lifes- extension [10], so that a resolved deficiency for this ele- pan, Adv. Ecol. Res. 27 (1997) 1-60. ment may explain the higher ability to produce fine [8] Helmisaari H.-S., Vitality of trees and forest ecosystems roots. On the same sites, liming tended to slightly but concepts and criteria, in: Andersson F., Braekke F., - significantly increase total number of mycorrhizal tips, Hallbäcken L. (Eds.), Imbalanced Forest Nutrition - Vitality but this depended mainly on the increase in fine root Measures. A SNS-project 1993-1996, Final and Work Report, length [2]. At the same time, there was an important shift Section of Systems Ecology, Swedish University of in ectomorphological morphotypes from smooth types Agricultural Sciences, 1997, p 158-175. with few or no hyphae towards hairy morphotypes with [9] Hüttl R.F., Die Nährelementversorgung geschädigter aggregated mycelium in wicks or cords. Hence, the Wälder in Europa und Nordamerika, Freib. Bodenkl. Abh. 28, uptake volume was not only increased after liming by University of Freiburg, Germany, 1991, 440 p. increased fine root length, but also as a result of the [10] Marschner H., Mineral Nutrition of Higher Plants, 2nd increase in mycelium [2]. This is in good agreement with ed., Academic Press, London, 1995. the relation between mycorrhizal associations and low [11]Olsthoorn A.F.M., Tiktak A., Fine root density and root phosphorus availability in acid mineral soils [10], which biomass of two Douglas-fir stands on sandy soils in the occur at most of the sites used in this study. Netherlands. 2. Periodicity of fine root growth and estimation of belowground carbon allocation, Neth. J. Agr. Sci. 39 (1991) 61-77. [12] Persson H., Majdi H., Clemensson-Lindell A., Effects 5. Conclusions of acid deposition on tree roots, Ecol. Bull. 44 (1995) 158-167. Puhe J., Persson H., Börjesson I., Wurzelwachstum und [13] In the fertility range of sites used in this study, moder- Wurzelschäden in Skandinavischen Nadelwäldern, Allg. Forst. ate doses of lime enhanced fine root biomass of oak both Zeitschr. 20 (1986) 488-492. in topsoil and in deeper horizons, and overall fertility [14] Raspe S., Fine root development, in: Hüttl R.F., Schaaf and nutrition were improved for Ca and Mg but not for P W. (Eds.), Magnesium Deficiency in Forest Ecosystems, and K. However, it is possible that the higher amount of Kluwer Academic Publishers, 1997, pp. 309-332. fine roots observed in the stands treated with lime, is not zur H- und Al- [15] Rost-Siebert K., Untersuchungen only an expression of a higher longevity and improved Toxizität an Keimpflanzen Fichte (Picea abies Karst.) und von
(Fagus sylvatica L.) in Lösungskultur. Berichte Buche [19] Van den Burg J., Olsthoorn A.F.M., National research Forschungszentrum Waldökosteme, Universität Göttingen 12 project on forest fertilisation. 1985/86-1991/92, IBN Research (1985) 1-219. Report 96/10, IBN-DLO, Wageningen, the Netherlands, 1996, 43 p. [16] Tennant D., A test of a modified line intersect method [20] Vogt K.A., Publicover D.A., Bloomfield J., Perez J.M., of estimating root length, J. Ecol. 63 (1975) 995-1001. Vogt D.J., Silver W.L., Belowground responses as indicators of [17] Trüby P., Eine Titrationsmethode zur simultanen environmental change, Environ. Exp. Bot. 33 (1993) 189-205. Bestimmung von H und Aluminium in NH + Cl-bodenextrak- 4 [21] Yin X., Perry J.A., Dixon R.K., Temporal changes in ten, Z. Pflanzenernähr. Bodenk. 152 (1989) 297-300. nutrient concentrations and contents of fine roots in a Quercus [18] Unistat Ltd, Unistat Version 4 for Windows, 1995. forest, For. Ecol. Manage. 44 (1991) 175-184.